The present invention relates to vibration actuators including electro-mechanical conversion elements that convert electrical energy into mechanical displacements. More particularly, the present invention relates to vibration actuators which reduce dampening of vibration due to particular placement of lead wires for electro-mechanical converting elements.
Vibration actuators generate elliptical motion on the surface of an elastic member by applying a drive signal to an electro-mechanical converting element, which is generally in the form of a piezoelectric member and attached to the elastic member. The electro-mechanical converting element harmoniously generates both a longitudinal vibration and a bending vibration. The vibration actuator then generates relative motion between the elastic member and a relative moving member that has been pressed against the elastic member during the above elliptical motion.
As for this type of vibration actuator, the analytical results are delineated, in detail, regarding the configuration and load characteristics thereof in "Piezoelectric Linear Motors for Application to Driving a Light Pick-Up Element," by Yoshiro Tomikawa, et al., 5th Symposium on Dynamics Related to Electromagnetic Force, Collected papers, pages 393-398. A self-propelled apparatus using this vibration actuator is also disclosed in "New Edition--Ultrasonic Motors" by Ueba and Tomikawa, published by Tricheps, pages 145-146.
FIG. 8 is an elevated perspective view of a conventional vibration actuator 100. As illustrated, thin plate-like piezoelectric members 102a and 102b, that are made of lead zirconate titanate ("PZT"), are adhered onto one of the planes of a rectangular, flat, plate-like elastic member 101. Piezoelectric members 102a and 102b generate a linear, longitudinal vibration, as well as biquadratic bending vibration, that expands and contracts in a longitudinal direction, i.e. along the longer sides of elastic member 101, in response to applied driving voltages. Driving force output members 101a and 101b are formed as projections at two of six locations of anti-nodes for the biquadratic bending vibration generated on elastic member 101. An elliptical motion, which is a synthesis of the longitudinal and bending vibrations, occurs on the end surfaces of driving force output members 101a and 101b.
A relative moving member (i.e. a moving element), not shown in FIG. 8, makes contact by being pressed with the end surfaces of driving force output members 101a and 101b. Subsequently, a relative motion is generated between elastic element 101 and the relative moving member in response to the above elliptical motion.
Vibration actuator 100 is designed such that the characteristic frequencies of the longitudinal vibration and the bending vibration that respectively occur on elastic member 101 attain extremely similar values. Consequently, by applying an A/C voltage that has a frequency similar to the two characteristic frequencies to piezoelectric members 102a and 102b, both a longitudinal vibration and a bending vibration may be generated harmoniously. This produces a relative motion between elastic member 101 and the relative moving member.
In vibration actuator 100, electrode 103a and electrode 103b are attached onto the surface of piezoelectric member 102a and piezoelectric member 102b, respectively. Electrical energy delivery members (lead wires) 104a and 104b are connected to a drive voltage generator and are soldered onto electrodes 103a and 103b. Subsequently, a drive voltage is applied to piezoelectric member 102a through lead wire 104a while a drive voltage is also applied to piezoelectric member 102b through lead wire 104b.
However, the locations of lead wires 104a and 104b with respect to electrodes 103a and 103b may vary depending upon the installation configuration of vibration actuator 100 and therefore the locations are not particularly specified. Moreover, as the soldering process is usually a manual operation, the locations of the soldering points may not be consistent. As a result, there is a problem of attenuation, i.e. reduction, of the bending vibration occurring on elastic member 101 depending upon the location of the soldering, thereby decreasing the drive efficiency of vibration actuator 100.
Additionally, there may be a problem of inconsistent soldering levels due to procedural discrepancies during the soldering process.